Volatile organic compounds (“VOC's”) are carbon-containing compounds that readily vaporize or evaporate into the air, where they may react with other elements or compounds to produce ozone. Ozone, in turn, causes air pollution and a host of health concerns including breathing problems, headache, burning, watery eyes and nausea, just to name a few. Some VOCs have also been linked to cancer, as well as kidney and liver damage.
VOC's are of particular concern in the paint and coatings industry in the manufacture and application of products using VOC's. Use of VOC's in the manufacture of paint and coatings result in poor plant air quality and worker exposure to harmful chemicals. Persons who are exposed to VOC's may suffer from a number of health problems, including but not limited to several types of cancers, impaired brain function, renal dysfunction and other health problems.
Similarly, painters and other users of VOC-containing paints and coatings who are regularly exposed to harmful VOC vapors may suffer from health problems. VOC-containing products release harmful VOC's into the air as they dry, especially with indoor applications. Indoor VOC levels are routinely 10 times higher than outdoor levels and may be up to 1,000 times higher immediately after painting. Further, although VOC levels are highest during and soon after painting, they continue seeping out for several years. In fact, only 50 percent of the VOC's may be released in the first year.
Accordingly, regulations have been implemented to protect manufacturing workers and end-users.
Paints and coatings having high VOC content are also considered environmental hazards. They are the second largest source of VOC emissions into the atmosphere after automobiles, responsible for roughly 11 billion pounds every year.
Consumers are demanding safer alternatives, and coatings formulators continue to be faced with the challenge of reducing VOC's, while, at the same time, providing a coating with required performance characteristics. Most often, formulators reduce the amount of, or replace, the most volatile components used in the coatings, which reduces VOC concerns to some extent, but may result in compromised performance. Desirably, a low VOC content paint or coating should have, at a minimum, equivalent performance to paints or coatings having higher VOC content. Toward that end, raw material suppliers continue to develop new, lower VOC products for use in paints and coatings, which do not compromise performance.
One typically volatile, but often very necessary component, used in coating compositions is the film-forming aid, i.e., coalescent, which allows a coatings formulator to use conventional, well-recognized latex emulsions that are lower in cost. Coalescents facilitate film formation, by softening dispersed polymers and allowing them to fuse or form a continuous film. The coalescent will then partially or completely volatilize out of the film, allowing the film to regain its original physical properties such as gloss and scrub resistance. Coalescents are selected that improve the properties of the paint/coating film, such as gloss, scrub resistance, and block resistance. Coalescents are also selected based upon a variety of properties, including without limitation, volatility, miscibility, stability, compatibility, ease of use, and cost. Traditional coalescents are highly volatile and can contribute significantly to the VOC content of a paint or coating.
As an alternative for achieving lower VOC content, polymeric emulsion systems that do not require these highly volatile film-forming aids are being developed. The polymers used in these newer emulsion systems tend to be soft enough to allow a low MFFT (minimum film forming temperature); however, certain performance parameters can sometimes suffer, and these softer emulsion systems are often expensive.
Film-forming aids are known in the art. Hydrophobic film-forming aids, such as the industry standard, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TXMB), partition to the polymer in the emulsion and soften dispersed particles of the emulsion during the coalescing phase of the application. The coalescent then partially or completely evaporates out of the film. By its nature, this “escaping” coalescent contributes significantly to the VOC's of the film, beginning with the coalescing phase and lasting for a sustained period afterwards. This, in turn, can affect the air quality around the film and be manifested as an unpleasant odor.
Because of these issues, there has been a trend toward developing and using less volatile, more permanent film-forming aids, such as plasticizers, for the coatings industry.
Plasticizers have been known and used for years as excellent coalescents for latex paints and other coatings. In some instances, they are also desired for their plasticizer function, because softening of a harder base polymer in the coating is often desired. It is also well-known that plasticizers can improve other paint performance characteristics, such as mud cracking, wet edge and open time. Plasticizers have a greater degree of permanence than other traditional coalescents, and in some instances the permanence of plasticizers can be a detriment. For coalescents, a balance must be struck between greater permanence—and thus lower VOC's—and good final film properties.
Phthalate plasticizers, such as di-n-butyl phthalate (DBP), diisobutyl phthalate (DIBP) or butyl benzyl phthalate (BBP), have traditionally been used in the coatings industry when a true plasticizer was required, as is the case when polymers with high Tg's (glass transition temperatures) are employed in one application or another. DBP and DIBP have a lower VOC content than traditional coalescents, but are still somewhat volatile, while BBP has a very low VOC content. Apart from VOC content, however, phthalate ester use has some disadvantages, as DBP and BBP uses, in particular, are restricted due to regulatory concerns.
Dibenzoate plasticizers have been recognized for various applications since about 1938. Their utility in coatings is also well known. Dibenzoates by their nature are non-phthalates and do not have the restrictions or health concerns associated with phthalates.
Monobenzoate ester coalescent technology has been developing and evolving since the 1980's, when isodecyl benzoate (IDB) was introduced to the coatings industry as a new, lower VOC coalescent. IDB has compatibility in a wide variety of polymers and was found to be an effective, low odor coalescent in latex paint formulations as compared to the traditional use of TXMB as the coalescent.
U.S. Pat. No. 5,236,987 to Arendt discloses the use of isodecyl benzoate, decyl benzoate, isooctyl benzoate, nonylbenzoate, and dodecyl benzoate as coalescents for latex paint.
At the beginning of the twenty-first century, 2-ethylhexyl benzoate (2-EHB) was launched as a new lower VOC film forming aid. 2-EHB was found to have greater efficiency than TXMB in many formulations, as well as lower odor. Isononyl benzoate (INB) was introduced in 2009 as a coalescent with a comparable formulated evaporation rate and efficiency to 2-EHB, while exhibiting a more effective MFFT lowering behavior than IDB.
Second generation benzoate ester coalescent technology has been developed with the less volatile dibenzoate esters. Dibenzoates can satisfy reduced VOC requirements where the volatilities of monobenzoate esters are considered too high. Dibenzoate technology, traditionally, is based on dipropylene glycol dibenzoate (DPGDB) and diethylene glycol dibenzoate (DEGDB) blends. Films formulated with these blends have been found to exhibit comparable performance properties to those formulated with TXMB, with improvements in scrub resistance, chemical resistance and enhanced open times.
Dibenzoate blends along with other components for use in lower VOC aqueous polymer coating compositions and other film-forming compositions are described in the art.
U.S. Pat. Publication No. 2008/0182929 to Strepka et al. discloses lower VOC content aqueous coating compositions containing dibenzoates of diethylene and dipropylene glycols in combination with at least one of the corresponding monoesters for the primary purpose of extending the open time exhibited by aqueous polymer compositions and, in part, to replace at least a portion of more volatile organic compounds typically used as coalescents.
U.S. Pat. Publication No. 2008/0076861 to Strepka et al. discloses a film-forming composition comprising at least one acrylic or vinyl acetate polymer or copolymer as a film forming ingredient and a blend of the benzoate of a 6-carbon monohydric alcohol, diethylene glycol dibenzoate, and diethylene glycol monobenzoate for use as a floor polish.
U.S. Pat. Publication No. 2011/0218285 discloses a low VOC coating additive employing a water dispersible polymer, a water insoluble plasticizer, cyclohexanedimethanol, and optionally an amphiphilic component for coatings to improve at least one performance characteristic of the coating, such as wet edge, open time, scrub resistance, wet adhesion and water resistance. Among the plasticizers disclosed are diethylene glycol dibenzoate, dipropylene glycol dibenzoate and tripropylene glycol dibenzoate.
Still, there is a need for continued efforts to improve plasticizer/coalescent technology to achieve minimal VOC's, while improving performance properties. A newer, next generation triblend of dibenzoate esters has been developed, which functions as well as traditional plasticizers or low VOC coalescents in coating applications, while achieving unexpectedly enhanced performance benefits in gloss and scrub resistance compared to current generation low VOC coalescent technology, including some enhancements over traditional dibenzoate blends.
A novel dibenzoate triblend plasticizer for use in low VOC paints and coatings has been developed. The present invention is directed to a blend of three dibenzoate plasticizers, DEGDB, DPGDB, and 1,2-propylene glycol dibenzoate (PGDB), that allows for low VOC coalescence, while yielding unexpectedly improved properties over the traditional dibenzoate blends. The inventive triblend is an improvement upon existing dibenzoate plasticizer technology used in paints and coatings and has not been previously known or used in paint and coatings applications. The 1,2-propylene glycol dibenzoate component was previously known for its use as a plasticizer, but not in the inventive blend disclosed herein. More specifically, 1,2-propylene glycol dibenzoate was known as a flavoring agent for beverages as described in U.S. Pat. No. 3,652,291 to Bedoukian.
The inventive triblend is particularly useful in latex and acrylic coating applications and provides improved gloss, freeze/thaw stability, scrub resistance, and chemical resistance and comparable open times over traditional dibenzoate plasticizer blends. The novel triblend is compatible with a large variety of material used in paints and other coatings. The novel triblend of DPGDB, DEGDB, and PGDB has not been utilized in paints and other coatings in the past.
The focus of the present invention is on the use of the inventive blend to formulate paints and other architectural and industrial coatings; however, the invention is not limited to these applications. The inventive plasticizer triblend can be used individually and in blends with other plasticizers in applications that include but are not limited to: adhesives, caulks, OEM coatings, plastisols, sealants, over print varnishes, polishes, inks, melt compounded vinyl, polysulfides, polyurethanes, epoxies, styrenated acrylics and combinations thereof.
It is an object of the invention to provide a film-forming aid having low VOC content, efficiency and compatibility when used in traditional latex emulsions or other polymeric coatings.
It is a further object of the invention to provide a polymeric emulsion paint or coating having a low VOC content and improved performance properties, including without limitation gloss, scrub resistance and chemical resistance, over that achieved with current low VOC emulsion paints and coatings.
It is yet another object of the invention to provide a low VOC content polymer emulsion paint or coating that is cost effective to produce and that is environmentally friendly, safe to handle, and not subject to regulatory control.